It is common to make foods pickled in rice bran paste (hereinafter referred to as bran pickles) at home. However, in order to make bran pickles having a good flavor, a mature rice bran paste must be prepared by carrying out pickling of foods such as vegetables and stirring of the bran paste every day for more than several months. Thus, it takes a lot of efforts to take care of rice bran paste.
In order to obtain foods having a flavor of bran pickles without using bran paste, a method has been proposed which comprises pickling foods such as vegetables in a pickling solution having a flavor of bran pickles, and a study has been made on the aromatic components and seasoning components of a mature rice bran paste [Nippon Nogeikagaku Kaishi, 57, 1113 (1983)]. However, a flavoring substance essential to a desirable bran pickles flavoring solution has not been specified yet, and thus there has not been established an industrial process for producing a bran pickles flavoring solution containing such a compound at a high concentration.
As aromatic components of bran paste, γ-lactones such as γ-dodecalactone, γ-dodecelactone and γ-decalactone are considered to be important. As for the production of precursors of γ-lactones, it is known that a lactic acid bacterium [Gastroenterology, 62, 430 (1972)], a bacterium belonging to the genus Corynebacterium [Agricultural and Biological Chemistry, 45, 2025 (1981)], a bacterium belonging to the genus Pseudomonas [Archives of Biochemistry and Biophysics, 99, 249 (1962)], etc. are capable of producing γ-dodecalactone precursor (10-hydroxyoctadecanoic acid).
Also known is a method for converting ricinoleic acid into γ-decalactone using yeast belonging to the genus Saccharomyces, etc. to improve the quality of castor oil containing ricinoleic acid (Japanese Published Unexamined Patent Application No. 66991/85, Japanese Published Unexamined Patent Application No. 100508/85). Further, it is known that γ-lactones can be produced by fermentation using Sporobolomyces oderus, Fusarium poae, etc. separately.
A clear bran pickles flavoring solution is preferred from the standpoint of commercial value, because the image of a flavoring solution as a commercial product is improved and there is no need for removing suspended matters such as rice bran from the obtained pickles.
Previous methods for producing a clear bran pickles flavoring solution include a method which comprises fermenting a dispersed solution of rice bran (hereinafter referred to as a bran suspension) and subjecting the fermented bran suspension to solid-liquid separation by a filter press, a rotary filter or a centrifuge to obtain a separated solution as a bran pickles flavoring solution. According to such methods, a clear bran pickles flavoring solution can be obtained. However, fat-soluble aromatic components such as γ-lactones are removed together with the residue in these methods, and therefore, a desirable bran pickles flavoring solution can not be obtained.
Further, when a fermented bran suspension is extracted with an aqueous solution of ethanol and the obtained extract is mixed with the above separated solution to obtain a bran pickles flavoring solution, the fatty acids extracted with an aqueous solution of ethanol are precipitated and suspended in the mixture, making the resulting flavoring solution turbid. Thus, a clear bran pickles flavoring solution can not be obtained.
There have been reported a process for producing a bran pickling composition by fermentation using a lactic acid bacterium, yeast and a Gram-negative bacterium such as a bacterium belonging to the genus Pseudomonas (Japanese Published Examined Patent Application No. 56852/82) and a process for producing a bran pickling composition by collecting aromatic components of bran pickles by steam distillation and then adding the collected components to the flavoring material (Japanese Published Examined Patent Application No. 50697/83), but neither of them is effective for producing a clear bran pickles flavoring solution.